1. Field of the Invention
The present invention pertains to an electronic starter for fluorescent lamps, in particular, an electronic starter employing a small quantity of components and being capable of adapting to different power specifications without having to change the circuitry.
2. Description of Related Art
The starting device, a critical component for ignition of fluorescent tubes, operates in conjunction with the ballast to produce high inverted potential necessary for turning on a fluorescent tube, which is the operating theory behind the conventional fluorescent lamps. The starting device has been transformed over the years from the mechanical type used in earlier days to the latest electronic type, the latter being capable of igniting the fluorescent tube in much shorter a time interval than the mechanical type. Most electronic starters now found on the market are based on the half-wave rectification model, such that the fluorescent tube often has to be ignited many times before it is successfully actuated. In spite of its relatively short preheating time required for the ignition, this could lead to the blackening of the fluorescent tube and also reduce the service life of the tube. Furthermore, the starters sometimes fail to ignite a fluorescent tube due to an insufficient preheating time. To correct the problem, a full-wave rectification starter is proposed to replace the conventional type of starters.
There is shown in FIG. 2 a schematic diagram of a conventional electronic starter employing a full-wave rectification connected to a fluorescent tube (51) and an AC power input (53), wherein the electronic starter comprises a bridge rectifier (50), a locking circuit (56), a power switch circuit (55), and a preheating circuit (54).
Both ends of the AC power input (53) are respectively connected to two input terminals of the fluorescent tube (51), where a ballast (52) is connected between one terminal of the AC power input (53) and one input terminal of the fluorescent tube (51). Two output terminals of the fluorescent tube (51) are respectively connected to two input terminals of the bridge rectifier (50) in the electronic starter, and two output terminals of the bridge rectifier (50) are respectively connected to the locking circuit (56), and the locking circuit (56) is connected through the power switch circuit (55) to the preheating circuit (54).
In the power switch circuit (55), when AC power for the electronic starter comes in through the bridge rectifier (50) after converting to DC, transistor Q3 is activated and transistor Q4 is cut off due to lower resistance at resistor R6 than R7. Because the resistance at resistor R4 is lower than R1, and the resistance at resistor R5 is lower than R2, after a certain time, the transistor Q2 is activated and transistor Q3 is then cut off. At the same time, transistor Q4 is activated and the voltage level at the drain of the transistor Q4 is dropped, thus the incoming current path for preheating the fluorescent tube (51) is completed. When a capacitor C1 at the base of the transistor Q1 is charged up to the conducting threshold voltage of the transistor Q1, the transistor Q1 becomes activated and transistor Q2 is cut off, thereafter transistor Q3 is activated again while transistor Q4 is cut off. Since transistor Q4 is disabled, the current path is cut off, causing the ballast (52) to produce high inverted potential for activating the fluorescent tube (51). After the fluorescent tube (51) is turned on, the locking circuit (56) can lock in the operating status of the power switch circuit (55).
Having described the conventional circuit design above, it is understood said electronic starting device employs more than two transistors and a MOSFET type transistor to control the preheating time and locking the operating status after igniting the fluorescent tube (51). Since a large number of components are required in its internal circuit, that means the cost is accordingly high for manufacturers of these starting devices. Eventually these starting devices would not be able to compete with other products of similar type due to its cost is higher than the other products. Also, the type of resistors and capacitors chosen decides the time constant for the transistor operation. Because each transistor has its own time constant, discrepancy in firing among transistors would easily occur, resulting in tube flickering.
The main object of the present invention is to provide an electronic starter that uses few components reducing the cost of the circuit and prevents the flickering of the fluorescent tube during ignition.
To achieve the above-mentioned objects, the electronic starter under the present invention comprises a full-wave rectification circuit connected through a fluorescent tube and a ballast to the AC power input, a preheating circuit for controlling the preheating time of the fluorescent tube, a power switch and locking circuit, connected in between the full-wave rectification circuit and the preheating circuit, for cutting off the power to the preheating circuit and locking the status of the preheating circuit in order to prevent flickering during preheating of the tube.
Other objects, advantages, and novel features will become more apparent from the following detailed description when taken in conjunction with the attached drawings.